1. Field of the Invention
This invention is concerned with means for imparting improved adhesion to a polyolefin, especially polypropylene, of substrates of acrylic-based or other protective polymers, in the form of a plastic film, sheet, or coating or a latex or solvent-based paint, ink, or coating by use of an intermediate layer, laminate, or veneer of a blend of segmented copolymer of a polyolefin and a poly(methacrylate) combined with a core/shell copolymer having a crosslinked rubber core. The invention may be further applied to improve adherence or adhesion of pressure-sensitive adhesives, which adhesives may serve to bond cloth, carpet, non-woven fabrics, plastics, and the like to the improved substrate. The invention is further concerned with means to an improved substrate for adherence of inks and colorants.
2. Description of the Prior Art
Matrix polymers, such as ABS, may be used as substrates for acrylic plastic sheet, film, coatings, inks, or latices, where the latter impart weatherability, decorative effects, printability, and the like, are useful in the assemblage of automobiles and other vehicles, such as automotive interiors, trunks (boots), truck (lorry) cabs, railroad car interiors, van (caravan) trim, and the like, equipment housing, furniture, and the like, where they offer advantages in cost and formability over metal or wood. Unfortunately, when an inexpensive matrix polymer, a polyolefin such as polypropylene or polyethylene, is used the acrylic polymers do not adhere well without special treatment, such as corona discharge or other oxidative treatments of the substrate. Acceptable adhesives or precoatings for the polyolefin prior to application of the acrylic polymer also are not readily available.
Acrylic polymers, more preferably polymers of methyl methacrylate, are useful for this purpose but are expensive and not as tough as certain plastic substrates used in the automotive and other industries. Such acrylic polymers are useful to achieve a combination of adhesion, toughness, and lower cost when combined with a cheaper, tougher polyolefin in a laminar structure (which structure may require a laminating adhesive in the case of polyolefins to prevent delamination), or when the surface of the polyolefin is altered to promote adhesion. This invention relates to improved methods for causing such lamination and/or adherence to occur. Solution of this problem allows combinations of inexpensive polyolefins to be protected, painted, printed, or adhered to in a manner to replace more expensive matrix polymers. Further, in many cases, no additional adhesive need be employed.
In U.S. Pat. No. 4,957,974 is disclosed the use of specific graft copolymers of polyolefins and polymethacrylates, when further blended with polypropylene, as useful for improving printability; the graft copolymers are disclosed as tie layers between otherwise incompatible polymers. In U.S. Pat. No. 5,035,933 is disclosed the use of such graft copolymers as tie layers between polyolefins and certain barrier polymers. These graft or segmented copolymers by themselves or blended with polyolefins, when based on a methyl methacrylate graft, have not been satisfactory in their ability to accept a paint with good adhesion against standard tests.
Thus the art has sought means for adherence of various forms of (meth)acrylic polymers to inexpensive polyolefin substrates as a means for protecting, coloring, or adhering to such polyolefins, without the use of expensive external physical treatment such as corona discharge. In the following text, "film" refers to a continuous plastic matrix less than about 10 mils (units) thick, whilst "sheet" refers to a continuous plastic matrix more than 10 mils (units) thick. "Predominately" has the meaning of at least about 50%.